How to render from multiple cameras in one go?
Assign the camera object to Scene.camera to make it the active cam of the scene:

import bpy

scn = bpy.context.scene

for obj in scn.objects:
    if obj.type == 'CAMERA':
        scn.camera = obj
        scn.render.filepath = obj.name
        bpy.ops.render.render(write_still=True)